A window cleaner has enough supplies to clean 21 windows per office building and the windows of a school with 42 windows. Altogether, there are enough supplies to clean 126 windows. How many office buildings can be washed?

Identify the equation that would be used to solve this problem algebraically.

A. [tex]21x - 42 = 126[/tex]

B. [tex]42x + 21 = 126[/tex]

C. [tex]42x - 21 = 126[/tex]

D. [tex]21x + 42 = 126[/tex]

To solve this problem, let's set up an equation to find out how many office buildings can be washed:

1. Identify Variables and Constants:
- Let [tex]\( x \)[/tex] be the number of office buildings.
- Each office building has 21 windows. Therefore, the total number of windows cleaned from office buildings is [tex]\( 21x \)[/tex].
- The school has 42 windows.
- In total, there are enough supplies to clean 126 windows.

2. Set Up the Equation:
- Combine the windows from the office buildings and the school: [tex]\( 21x + 42 \)[/tex].
- This must equal the total number of windows, which is 126:
[tex]\[ 21x + 42 = 126 \][/tex]

3. Choose the Correct Equation:
- The equation that represents this situation is [tex]\( 21x + 42 = 126 \)[/tex].

4. Solve the Equation (if required):
- You can solve for [tex]\( x \)[/tex] to find how many office buildings can be washed, but the problem primarily asks to identify the equation.

Therefore, the answer to the problem is: the equation used to solve this problem is [tex]\( 21x + 42 = 126 \)[/tex].